Mixed green-emitting phosphor and cathode ray tube using the same

ABSTRACT

A mixed green-emitting phosphor manufactured by mixing about 20 to 60 weight percent of Y3(Al,Ga)5O12:Tb phosphor, less than about 30 weight percent of LaOCl:Tb phosphor, less than about 60 weight percent of Y2SiO5:Tb phosphor, and less than about 20 weight percent of Zn2SiO4:Mn phosphor and a cathode ray tube employing it are disclosed. The luminance characteristic is excellent under a high current density.

BACKGROUND OF THE INVENTION

The present invention relates to a mixed green-emitting phosphor and acathode-ray tube using the same, and in more detail, to a mixedgreen-emitting phosphor for use in a projection cathode-ray tube whichhas an excellent luminance saturation characteristic under high currentdensity and a cathode-ray tube using the same.

In a green-emitting phosphor for use in a general cathode-ray tube,ZnS-based phosphors, such as ZnS:Cu,Au,Al phosphor, ZnS:Cu,Al phosphor,etc., are generally used.

However, cathode-ray tubes which are operated under high current densityand high voltage drive have recently attracted much attention ascathode-ray tubes become large and high-definition. Therefore, aphosphor of high luminance especially under high current density, isneeded. However, since the conventional ZnS-based phosphors are unableto provide sufficient luminance effects under high current density, therare earth phosphors have been used recently.

As examples of rare earth green-emitting phosphors which are activatedunder high current density, such as in the projection cathode-ray tube,Y₃(Al,Ga)₅O₁₂:Tb phosphor, InBO₃:Tb phosphor, Y₂SIO₅:Tb phosphor,LaOCl:Tb phosphor, Zn₂SiO₄:Mn phosphor, or mixtures thereof can beenumerated.

The Y₃(Al,Ga)₅O₁₂:Tb phosphor has good current-luminance saturationcharacteristics and high emitting luminance.

The Y₂SiO₅:Tb phosphor is known as having high color purity, shortafterglow time and, especially, good luminance saturationcharacteristics.

For the LaOCl:Tb phosphor, it has good current-luminance saturationcharacteristics and high color purity.

Zn₂SiO₄:Mn phosphor is known as not having good luminance saturation andafterglow characteristics, but having excellent color purity.

The InBO₃:Tb phosphor has a high resistance under high current density,is suitable for use in the projection cathode-ray tube, and has goodcolor purity. Meanwhile, the afterglow time is long so as to mix withthe phosphor whose afterglow time is short when applied to a cathode-raytube.

There are many mixed green-emitting phosphors prepared by mixing theabove-mentioned rare earth-based phosphors. As one example, U.S. Pat.No. 4,924,139 discloses a mixed phosphor of InBO₃:Tb withY₃(Al,Ga)₅O₁₂:Tb whose color purity is excellent and whose afterglowtime is short.

However, the above mentioned phosphors and the mixed phosphors thereofhave undesirable luminance saturation and deterioration characteristics.Accordingly, there are many problems that should be improved in theknown phosphors.

SUMMARY OF THE INVENTION

It is an object of the present invention, for improving the problemsoccurring when the phosphors are activated under high current density,to provide a mixed green-emitting phosphor which has excellent luminancesaturation characteristics and deterioration characteristics, by mixingphosphors having excellent characteristics but without using InBO₃:Tbphosphor.

It is another object of the present invention to provide a cathode raytube whose luminance and luminance saturation characteristics are verygood, and which is manufactured using the mixed green-emitting phosphorof the present invention.

To accomplish the above-mentioned first object, there is provided in thepresent invention, a mixed green-emitting phosphor manufactured bymixing and containing Y₃(Al,Ga)₅O₁₂:Tb, LaOCl:Tb, Y₂SiO₅:Tb andZn₂SiO₄:Mn phosphors in the following concentrations: about 20 to 60weight percent of Y₃(Al,Ga)₅O₁₂:Tb phosphor, no more than about 30weight percent of LaOCl:Tb phosphor, no more than about 50 weightpercent of Y₂SiO₅:Tb phosphor, and no more than about 20 weight percentof Zn₂SiO₄:Mn phosphor.

Desirably, the mixed green-emitting phosphor is manufactured by mixingand contains Y₃(Al,Ga)₅O₁₂:Tb, LaOCl:Tb, Y₂SiO₅:Tb and Zn₂SiO₄:Mnphosphors in amounts of: about 20 to 50 weight percent ofY₃(Al,Ga)₅O₁₂:Tb phosphor, no more than about 20 weight percent ofLaOCl:Tb phosphor, no more than about 40 weight percent of Y₂SiO₅:Tbphosphor, and no more than about 10 weight percent of Zn₂SiO₄:Mnphosphor.

The first object of the present invention can be also accomplished by amixed green-emitting phosphor manufactured by mixing and containingY₃(Al,Ga)₅O₁₂:Tb, Y₂SiO₅:Tb and Zn₂SiO₄:Mn phosphors in the followingconcentrations: about 20 to 60 weight percent of Y₃(Al,Ga)₅O₁₂:Tbphosphor, no more than about 60 weight percent of Y₂SiO₅:Tb phosphor,and no more than about 20 weight percent of Zn₂SiO₄:Mn phosphor withoutusing LaOCl:Tb phosphor.

When three phosphors as mentioned above are mixed so as to manufacturethe mixed phosphor of the present invention, an excellent effect alsocould be obtained, though using up to about 60 weight percent ofY₂SiO₅:Tb phosphor.

Desirably, the mixed green-emitting phosphor is manufactured by mixingand contains Y₃(Al,Ga)₅O₁₂:Tb, Y₂SiO₅:Tb and Zn₂SiO₄:Mn phosphors inamounts of: about 30 to 60 weight percent of Y₃(Al,Ga)₅O₁₂:Tb phosphor,no more than about 50 weight percent of Y₂SiO₅:Tb phosphor, and no morethan about 10 weight percent of Zn₂SiO₄:Mn phosphor.

The other object of the present invention is accomplished by acathode-ray tube having fixed to a surface thereof a mixedgreen-emitting phosphor manufactured by mixing and containingY₃(Al,Ga)₅O₁₂:Tb, LaOCl:Tb, Y₂SiO₅:Tb and Zn₂SiO₄:Mn phosphors inamounts of: about 20 to 60 weight percent of Y₃(Al,Ga)₅O₁₂:Tb phosphor,no more than about 30 weight percent of LaOCl:Tb phosphor, no more thanabout 50 weight percent of Y₂SiO₅:Tb phosphor, and no more than about 20weight percent of Zn₂SiO₄:Mn phosphor.

The other object of the present invention can be also accomplished by acathode-ray tube comprising a mixed green-emitting phosphor manufacturedby mixing and containing Y₃(Al,Ga)₅O₁₂:Tb, Y₂SiO₅:Tb and Zn₂SiO₄:Mnphosphors in the following concentrations: about 20 to 60 weight percentof Y₃(Al,Ga)₅O₁₂:Tb phosphor, no more than about 60 weight percent ofY₂SiO₅:Tb phosphor, and no more than about 20 weight percent ofZn₂SiO₄:Mn phosphor.

DETAILED DESCRIPTION OF THE INVENTION

A phosphor of the present invention, as a green-emitting phosphormanufactured by mixing three or four phosphors, is manufactured so as tohave excellent characteristics by keeping the merits of each phosphorwhile mutually complementing their drawbacks.

The characteristics of each green-emitting phosphor used inmanufacturing the mixed phosphor of the present invention is describedin the following Table 1.

TABLE 1 luminance color afterglow life luminance saturation purity timetime Y₃(Al₂Ga)₅O₁₂:Tb ◯ ◯ x ◯ ◯ LaOCl:Tb Δ ◯ ◯ ◯ ◯ Y₂SiO₅:Tb Δ ⊚ ◯ ◯Zn₂SiO₄:Mn ◯ x ⊚ x x * ⊚: excellent ◯: good Δ: normal x: poor

The mixed green-emitting phosphor of the present invention, inconsideration of the above-mentioned merits and drawbacks of eachphosphor, is obtained by selecting and then mixing each phosphor in aproper mixing ratio. Accordingly, choice of the mixing ratio of eachphosphor is very important. The mixing amount of each phosphor isdefined by the following.

When the mixing amount of Y₃(Al,Ga)₅O₁₂:Tb phosphor is less than about20 weight percent, the luminance characteristics of the mixed phosphoris undesirably reduced. When the amount is more than about 60 weightpercent, the characteristics of the color purity is reduced.Accordingly, the mixing amount of the Y₃(Al,Ga)₅O₁₂:Tb phosphor shouldbe within the range of about 20 to about 60 weight percent.

When the mixing amount of the LaOCl:Tb phosphor is more than about 30weight percent, the luminance and the luminance saturationcharacteristics of the mixed phosphor decrease. Accordingly, the mixingamount of the LaOCl:Tb phosphor should be more than O and less thanabout 30 weight percent.

For the Y₂SiO₅:Tb phosphor, when the mixing amount is more than 50weight percent, the luminance saturation characteristics are improved.Meanwhile, the initial luminance is reduced. Accordingly, the mixingamount of this phosphor should be more than 0 but not more than about 50weight percent.

Moreover, when the mixing amount of the Zn₂SiO₄:Mn phosphor is more thanabout 20 weight percent, the color purity and the initial luminance areimproved. Meanwhile, the deterioration and the luminance saturationcharacteristics are reduced. Accordingly, the amount should be more thanO but not more than about 20 weight percent.

Each phosphor used to manufacture the mixed phosphor of the presentinvention is prepared according to the following methods.

1) Manufacture of a Y₃(Al,Ga)₅O₁₂:Tb phosphor

100 g of yttrium oxide (Y₂O₃), 52.7 g of aluminum oxide (Al₂O₃), 41.5 gof gallium oxide (Ga₂O₃), 10 g terbium oxide(Tb₄O₇), and 7 g of bariumfluoride (BaF₂) are homogeneously mixed and then fired at 1450 to 1550°C. for one to three hours. After cooling the fired mixture, washing anddrying gives Y₃(Al,Ga)₅O₁₂:Tb phosphor.

2) Manufacture of a LaOCl:Tb phosphor

To mix 100 g of lanthanum oxide (La₂O₃) and 15 g of terbium oxide(Tb₄O₇) homogeneously, they are dissolved in a proper amount of nitricacid. Then an oxalic acid coprecipitate of La and Tb using 70 g ofoxalic acid is manufactured. After drying the obtained coprecipitate,first-firing at about 1000° C., then dry-mixing with 50 g of NH₄Cl,second-firing at about 450° C. in a furnace, and then third-firing at1000 to 1200° C. under a reducing atmosphere for about two hours,washing and drying give the LaOCl:Tb phosphor.

3) Manufacture of a Y₂SiO₅:Tb phosphor

100 g of Yttrium oxide (Y₂O₃), 12 g of silicon dioxide (SiO₂), 10 g ofterbium oxide (Tb₄O₇), and 7 g of barium fluoride (BaF₂) arehomogeneously mixed and fired at about 1200 to 1400° C. for one to threehours under a weak reducing atmosphere. After washing the firedmaterial, drying gives the Y₂SiO₅:Tb phosphor.

4) Manufacture of a Zn₂SiO₄:Mn phosphor

40 g of zinc oxide (ZnO), 60 g of silicon dioxide (SiO₂), and 2 g ofmanganese sulfate (MnSO₄) are mixed and fired at 1250 to 1300° C. fortwo to four hours. Washing and drying the fired material give theZn₂SiO₄:Mn phosphor.

Four fluorescent materials obtained as mentioned above are mixed in thepredetermined percent by weight, based on the total weight of the mixedphosphor, so as to give the mixed green-emitting phosphor of the presentinvention. The mixing percentages of each sample according to someembodiments of the present invention are illustrated in Table 2.

TABLE 2 phosphor (percent wt./wt.) sample A B C D E #1 65 5 30 #2 50 2020 10 #3 40 20 30 10 #4 30 20 40 10 #5 20 20 50 10 #6 50 10 30 10 #7 4030 20 10 #8 40 30 25 5 #9 40 20 25 15  #10 60 10 20 10  #11 60 30 10 #12 50 40 10  #13 40 50 10  #14 30 60 10  #15 40 50 10  #16 40 40 20

In Table 2, phosphor A is Y₃(Al,Ga)₅O₁₂:Tb, phosphor B is LaOCl:Tb,phosphor C is Y₂SiO₅:Tb, phosphor D is Zn₂SiO₅:Mn, and phosphor E isInBO₃:Tb.

Using each sample, projection cathode-ray tubes are manufacturedaccording to the conventional method and the emitting characteristicsaccording to the mixing ratio of each phosphor are measured, which areshown in Table 3. For reference, the x coordinate is less than 0.350 andthe y coordinate is more than 0.550 in the chromaticity coordinate forthe green color.

TABLE 3 Lu- min- ance luminance sat- (ft · L) with relation to currentura- chromic sam- 200 350 500 900 1200 tion coordinates ples (μA) (μA)(μA) (μA) (μA) (γ) x y #1 2521 4263 7930 10460 13298 0.879 0.3219 0.5925#2 2561 4341 8031 11910 14514 0.945 0.3198 0.5954 #3 2554 4318 802211940 14916 0.960 0.3188 0.5961 #4 2526 4292 8010 11891 14671 0.9680.3160 0.6002 #5 2496 4208 7981 11819 14616 0.976 0.3150 0.6008 #6 25434296 8070 11892 14678 0.962 0.3291 0.5891 #7 2547 4301 7892 11804 144110.943 0.3201 0.5996 #8 2510 4280 7801 11782 14339 0.952 0.3301 0.5871 #92601 4344 8042 11926 14529 0.931 0.3154 0.6011 #10 2571 4308 8030 1197614593 0.946 0.3214 0.5908 #11 2561 4301 8113 12018 14813 0.964 0.32940.5887 #12 2554 4298 8115 12084 14864 0.970 0.3292 0.5888 #13 2549 42948109 12106 14973 0.979 0.3274 0.5981 #14 2541 4288 8110 12096 149560.981 0.3251 0.5986 #15 2611 4321 8101 11840 14475 0.924 0.3111 0.6118#16 2623 4336 8111 11821 14463 0.919 0.3144 0.6109 *The value of thecurrent was increased from 200 to 1200 μA at a voltage of 32 kV andsimultaneously the luminance was measured, thereby computing the valueof the luminance saturation (γ) according to the following formula.$\gamma = {\frac{{luminance}\quad {at}\quad 1200\quad {µA}}{{luminance}\quad {at}\quad 200\quad {µA}} \times \frac{1}{6}}$

*The color coordinates are the values at 350 μA. *The characteristicvalues of each emitting are at the voltage of 32 kV and in the rastersize of 122 × 69 mm²

As shown in Table 2, the phosphor layer manufactured by using the mixedphosphor of the present invention has excellent phosphor layercharacteristics. Particularly, the result for sample #1, including theInBO₃:Tb phosphor, shows that luminance characteristics are not goodunder high current density. Meanwhile, samples #2-#16, as the mixedphosphors of the present invention, have excellent luminancecharacteristics under high current density, and are better than theconventional phosphor whose luminance saturation is 0.879 whenconsidering the value of the luminance saturation which is from 0.931 to0.981. From the result of the cathode-ray tube employing the samples#11-#16, it is confirmed that the phosphor mixed with three phosphorswithout the LaOCl:Tb phosphor also have excellent effects.

What is claimed is:
 1. A mixed green-emitting phosphor comprising Y₃(Al,Ga)₅O₁₂:Tb, LaOCl:Tb, Y₂SiO₅:Tb and Zn₂SiO₄:Mn phosphors in thefollowing concentrations by weight: 20 to 60% of Y₃(Al, Ga)₅O₁₂:Tb, nomore than 30% of LaOCl:Tb, no more than 50% of Y₂SiO₅:Tb, and no morethan 20% of Zn₂SiO₄:Mn.
 2. A mixed green-emitting phosphor according toclaim 1 comprising: 20 to 50% of Y₃(Al, Ga)₅O₁₂:Tb, no more than 20% ofLaOCl:Tb, no more than 40% of Y₂SiO₅:Tb, and no more than 10% ofZn₂SiO₄:Mn.
 3. A mixed green-emitting phosphor according to claim 1wherein said phosphor is free of InBO₃:Tb phosphor.
 4. A mixedgreen-emitting phosphor comprising Y₃(Al,Ga)₅O₁₂:Tb phosphor, Y₂SiO₅:Tbphosphor and Zn₂SiO₄:Mn phosphor in the following concentrations byweight: 20 to 60% of Y₃(Al, Ga)₅O₁₂:Tb, no more than about 60% ofY₂SiO₅:Tb, and no more than 20% of Zn₂SiO₄:Mn.
 5. A mixed green-emittingphosphor according to claim 4 comprising: 30 to 60% of Y₃(Al,Ga)₅O₁₂:Tb, no more than 50% of Y₂SiO₅:Tb, and no more than 10% ofZn₂SiO₄:Mn.
 6. A mixed green-emitting phosphor according to claim 4wherein said phosphor is free of InBO₃:Tb phosphor.
 7. A cathode-raytube of high luminance including a mixed green-emitting phosphorcomprising Y₃(Al,Ga)₅O₁₂:Tb, LaOCl:Tb, Y₂SiO₅:Tb and Zn₂SiO₄:Mnphosphors in the following concentrations by weight: 20 to 60% of Y₃(Al,Ga)₅O₁₂:Tb, no more than 30% of LaOCl:Tb, no more than 50% of Y₂SiO₅:Tb,and no more than 20% of Zn₂SiO₄:Mn fixed on a surface of a cathode-raytube.
 8. A cathode-ray tube of high luminance according to claim 7wherein said mixed green-emitting phosphor is free of InBO₃:Tb phosphor.9. A cathode-ray tube of high luminance including a mixed green-emittingphosphor comprising Y₃(Al,Ga)₅O₁₂:Tb, Y₂SiO₅:Tb, and Zn₂SiO₄:Mnphosphors in the following concentrations by weight: 20 to 60% of Y₃(Al,Ga)₅O₁₂:Tb, no more than 60% of Y₂SiO₅:Tb, and no more than 20% ofZn₂SiO₄:Mn fixed to a surface of a cathode-ray tube.
 10. A cathode-raytube of high luminance according to claim 9 wherein said mixedgreen-emitting phosphor is free of InBO₃:Tb phosphor.
 11. A method offorming a mixed green-emitting phosphor comprising mixing Y₃(Al,Ga)₅O₁₂:Tb, LaOCl:Tb, Y₂SiO₅:Tb and Zn₂SiO₄:Mn phosphor in the followingconcentrations by weight: 20 to 60% of Y₃(Al, Ga)₅O₁₂:Tb, no more than30% of LaOCl:Tb, no more than 50% of Y₂SiO₅:Tb, and no more than 20% ofZn₂SiO₄:Mn and forming a mixed green phosphor.
 12. A method of forming amixed green-emitting phosphor according to claim 11 wherein saidphosphor is free of InBO₃:Tb phosphor.
 13. A method of forming a mixedgreen-emitting phosphor comprising mixing Y₃(Al,Ga)₅O₁₂:Tb phosphor,Y₂SiO₅:Tb phosphor and Zn₂SiO₄:Mn phosphor in the followingconcentrations by weight: 20 to 60% of Y₃(Al, Ga)₅O₁₂:Tb, no more than60% of Y₂SiO₅:Tb, and no more than 20% of Zn₂SiO₄:Mn and forming a mixedgreen phosphor.
 14. A method of forming a mixed green-emitting phosphoraccording to claim 13 wherein said phosphor is free of InBO₃:Tbphosphor.